The overall goal of this project is to understand the role of oxygen derived radical (ODR) on cardiac injury during ischemia and postischemic injury. A major focus of the current proposal is to understand the role of hydroxyl radical (OH) and singlet oxygen (O2) in the pathogenesis of ischemic injury and their effect on adenosine-mediated protection in the ischemic heart. We are proposing that (1) both OH and O2 are generated during postischemic in the reperfusion and that O2 is much more toxic than OH. We will directly investigate O2 production during postischemic reperfusion with electron paramagnetic spin resonance spectroscopy (EPR) and HPLC, correlate it with resultant injury quantitatively and study the intracellular mechanisms leading to O2 formation from H2O2 or OH. We also propose that isolated myocytes and endothelial cells (EC) produce OH and O2 during post-anoxic reoxygenation and this production is primarily linked to metabolic abnormalities and the resumption of mitochondrial respiration. Finally, the contribution of endothelial cells towards ischemic injury to myocytes will be investigated with the coculture of EC and myocytes. The second major emphasis is on the role of adenosine in protection against I/R. It is proposed that adenosine and its analogs inhibit ODR generation via receptor-mediated mechanisms. Oxygen-derived radicals inhibit the nucleotidase activity and adenosine production which has deleterious effect on cell viability during I/R. We further plan to test the hypothesis that ischemic myocytes release various nucleosides which are catabolized by EC xanthine oxidase resulting in ODR injuries to myocytes. This will be done in both isolated hearts and coculture of myocytes and endothelial cells. Experiments proposed utilizing isolated cultured myocytes and EC will allow us to study the direct effect of OH and O2 and progressive stages in the process of cell death and their effect on the adenosine-mediated cardioprotection. Direct knowledge of ischemic cell injury caused by OH and O2 and their harmful effect on adenosine-mediated beneficial actions will be important in the development of new improved strategies to retard or prevent myocardial injury in man.